This invention relates to an etchant for providing textured silicon surfaces and to a method therefor. More paticularly, this invention relates to a new preferential etchant for reducing the reflectivity of silicon solar cell surfaces.
Solar cell efficiency is enhanced if the reflectivity of the silicon surface is reduced in order to increase the amount of light absorbed by the cell. Prior art researchers have recognized the desirability of altering silicon surfaces, preferably by chemical etching. For example, the paper titled "V-Grooved Silicon Solar Cells" by Cosmo R. Baraona and Henry W. Brandhorst, NASA TM X-71715, presented at the 11th Photovoltaic Specialist Conference sponsered by IEEE at Phoenix, Ariz., May 6-8, 1975, reports the results of using two different etchants on silicon solar cell surfaces. While one of the preferential etchants, hydrazine hydrate, did provide the desired velvet texturized surface, this etch is undesirable from a safety viewpoint. Efforts to employ the more attractive potassium hydroxide etch were unsuccessful. Thus, by using photomasks, and a near boiling potassium hydroxide-water mixture, grooved and gridded surfaces having some improvement over polished surfaces with respect to total reflection were obtained. However, the improvement in reflection was not sufficient to consider this a feasible approach. The use of a potassium hydroxide etch on unmasked silicon resulted in a shiny surface which was ineffective for reducing reflection. Thus, there is still a need for a practical and effective etch to provide the texturized surfaces found to be desirable in solar cells.